CLOUDIFY-2251

1.host_init set a "agent plugin installed" state on the host using the kv_store plugin.
2.execute_operation will do a fast verification the existence of the plugin and its operation, if failed, it will wait until all plugins are installed by waiting for "agent plugin installed" state. once all are installed it will verify existence again, if failed it will raise an exception.
3. split plugin verfication and operation method argument fetching into two seperate operations.
CLOUDIFY-2251

Add test that an exception is thrown when an operation which the plugin doesn't implement is used.
ignore intellij project